docs: def bend_rounded_Ito(Di, angle, Re, rc=None, bend_diameters=None, 
                       roughness=0.0):
      '''Ito method as shown in Blevins. Curved friction factor as given in 
      Blevins, with minor tweaks to be more accurate to the original methods.
      '''
      if not rc:
          if bend_diameters is None:
              bend_diameters = 5.0
          rc = Di*bend_diameters
      
      radius_ratio = rc/Di
      angle_rad = radians(angle)
      De2 = Re*(Di/rc)**2.0
      if rc > 50.0*Di:
          alpha = 1.0
      else:
          # Alpha is up to 6, as ratio gets higher, can go down to 1
          alpha_45 = 1.0 + 5.13*(Di/rc)**1.47
          alpha_90 = 0.95 + 4.42*(Di/rc)**1.96 if rc/Di < 9.85 else 1.0
          alpha_180 = 1.0 + 5.06*(Di/rc)**4.52
          alpha = interp(angle, _Ito_angles, [alpha_45, alpha_90, alpha_180])
      
      if De2 <= 360.0:
          fc = friction_factor_curved(Re=Re, Di=Di, Dc=2.0*rc,
                                      roughness=roughness,
                                      Rec_method='Srinivasan', 
                                      laminar_method='White',
                                      turbulent_method='Srinivasan turbulent')
          K = 0.0175*alpha*fc*angle*rc/Di
      else:
          K = 0.00431*alpha*angle*Re**-0.17*(rc/Di)**0.84
      return K